The present invention relates generally to the art of air cooling of high power vacuum tubes, and more particularly to a system for reducing aerodynamic drag in the path of air flow through the system so as to increase the cooling capacity of the system.
High power broadcasting stations, such as AM, FM, and TV broadcasting stations, conventionally employ large, high power vacuum tubes in the output stage of the transmitter for amplifying the modulated RF signal which is to be transmitted. These vacuum tubes conventionally operate at an extremely high power levels, measured in tens of kilowatts. Since the tubes are, of course, not 100% efficient, a portion of this high power is converted into heat in the tube. Some means must therefore be provided to dissipate this unwanted heat.
These high power vacuum tubes generally have a cylindrical body configuration, with a large number of heat radiating fins extending radially outward from the body. These fins, which all have approximately the same length, are joined at their outer extremities by a wall, which thus has a generally cylindrical configuration and is coaxially disposed about the axis of the vacuum tube body. An air channel is thereby defined between the body of the vacuum tube and the cylindrical wall joining the extremities of the heat radiating fins.
High power vacuum tubes of this type are generally air cooled by forcing large volumes of air through this air channel. The size of the fan used to generate this air flow must, of course, be selected in accordance with the cooling requirements of the vacuum tube being used. For those transmitters using very high power output stages, cooling fans having a very high capacity must be employed. Effective cooling of the tube is critical, since the useful life of the tube is adversely affected by operation at elevated temperatures. It would therefore be desireable to provide greater cooling of the tube so that it operates at a lower temperature and thus has a longer useful life.